(CNN) --Saddam Hussein's capture caused a sharp spike in President Bush's approval ratings, according to the results of a CNN/USA Today/Gallup Poll released Wednesday.

The president also had a lead of more than 20 percentage points over Democratic front-runner Howard Dean in a hypothetical matchup among registered voters, the poll found.

In the battle for the Democratic nomination, the former Vermont governor still outdoes his eight rivals, but poll results show that Saddam's arrest may have blunted the candidate's momentum somewhat after he won an endorsement from former Vice President Al Gore.

Among poll respondents interviewed Monday and Tuesday, 63 percent said they approved of Bush's job performance, while 34 percent disapproved. The approval rating is Bush's highest since June and is a significant gain over his rating of 50 percent a month ago.

By contrast, in a poll done Thursday to Saturday, before news of the capture broke, Bush's approval was 54 percent, with 43 percent expressing disapproval.

The margin of error is plus or minus 3 percentage points for the most recent survey.

The poll also showed that Americans are increasingly supportive of, and optimistic about, the U.S. effort in Iraq.

About six out of 10 respondents said it was worth going to war. A majority also think Bush has a clear plan for Iraq and that the war has made the United States safer from terrorism.

The poll showed that Dean -- who has boosted his candidacy with opposition to the Iraq war -- trails Bush head-to-head among registered voters.

Bush leads 60 percent to 37 percent, with a margin of error of plus or minus 4 percentage points, the survey found. In polling directly before Saddam's capture, Bush was ahead of Dean 52 percent to 44 percent.

The new poll also showed retired Army Gen. Wesley Clark, another Democratic hopeful, running better against the president than Dean. Bush is still ahead of Clark among registered voters, 56 percent to 40 percent, the survey said.

Bush also leads Sen. Joseph Lieberman of Connecticut 59 percent to 38 percent in a contest among registered voters, according to the poll.

In a CNN/USA Today/Gallup Poll taken the week before Gore's endorsement, Dean's support stood at 25 percent among registered Democratic voters.

It rose to 33 percent after Gore gave his seal of approval December 10 to the candidate. But in the polling after Saddam's capture, support for Dean had retreated to 27 percent.

The margin of error for poll results among registered voters who say they are Democrats or lean Democratic was plus or minus 5 percentage points.

In the latest poll, Lieberman and Clark ranked second behind Dean, tied at 12 percent among registered Democratic voters. Rep. Dick Gephardt of Missouri and Sen. John Kerry of Massachusetts followed, tied at 7 percent each.

Political observers speculate about what impact Saddam Hussein's arrest will have on U.S. politics.

Lieberman, Gore's running mate in 2000, has seen a slight increase in support since the former vice president decided to back Dean, rising from 10 percent to 12 percent. However, that number is within the poll's margin of error.

The poll also showed a continuation of a steady decline in support for Clark since the former NATO supreme commander entered the race with much fanfare in September.

After announcing his candidacy, Clark ranked first in the crowded field, with 22 percent backing in a poll. But his support has dropped by nearly half.

Seventeen percent of registered voters who say they are either Democrats or lean Democratic remain undecided a month before the Iowa caucuses, the poll found.